1. Technical Field
The present disclosure relates to a touch detection device, a display device with a touch detection function, and an electronic apparatus which enable an external approaching object to be detected in response to a change in capacitance.
2. Description of the Related Art
In recent years, attention has been focused on a display device with a touch detection function which has a touch detection device or a so-called touch panel provided on a display device such as a liquid crystal display device or which has a touch detection device and a display device integrated with each other. On the display device are displayed various types of button images or the like to replace typical mechanical buttons, thereby enabling entry of information. The display device having such a touch panel requires no input devices like a keyboard, a mouse, or key pads, and thus has been extensively used, for example, with personal digital assistants like mobile telephones in addition to computers.
There are several touch detection operation systems such as of the optical and resistive types; however, in particular, for example, portable terminals tend to employ the capacitive type which provides a relatively simple structure and requires lower power consumption. In the capacitive touch detection device, capacitance is formed between drive electrodes to which a drive signal is applied. The capacitive touch detection device detects whether there is a touch or not by detecting a change in capacitance caused by an external object being brought into contact with or proximity to the device, that is, a change in voltage waveform that appears on the touch detection electrodes.
Some of such capacitive touch detection devices are provided with two fixed threshold values in order to produce three values by comparing these threshold values with a detected change in capacitance, thereby calculating a first region in which a change in capacitance equal to or greater than the higher threshold value is detected and a second region in which a change in capacitance equal to or greater than the lower threshold value and less than the higher threshold value is detected (see Japanese Patent Application Laid-Open Publication No. 2010-55510 (JP-A-2010-55510)). Further, the touch detection device disclosed in JP-A-2010-55510 determines a point as the one at which a user intended to be in contact with or in close proximity to the panel surface, the point being offset by a predetermined amount from the area barycenter of the first region on a straight line connecting between the area barycenter of the first region and the area barycenter of the second region. As described above, the touch detection device disclosed in JP-A-2010-55510 attempts to approximate to the contact point or proximity point intended by a user on the panel surface using the area barycenters of the two regions obtained by the threshold determination process.
However, the touch detection device disclosed in JP-A-2010-55510 deals with three groups of values by two threshold values and only classifies detected signals into the first region and the second region; that is, it is only determined to which of the two regions the level of a signal at each point on the touch surface belongs. Thus, in the touch detection device that employs a method for determining a touch point on the panel surface based on the area barycenter of such a region, there is a possibility that a difference between the determined touch point and the contact point or proximity point intended by a user occurs, thus possibly preventing improvement in the control accuracy by a user.
For the foregoing reasons, there is a need for a touch detection device, a display device with a touch detection function, and an electronic apparatus which can improve the accuracy of control by a user's touch operation on the screen.